It has surprisingly been found that certain condensation products of formaldehyde with diprimary aliphatic or cycloaliphatic diamines, which are described in more detail below, are particularly suitable for use as latent, moisture-activatable hardeners for polyisocyanates. One particularly remarkable feature of these condensation products is that, on the one hand, they are largely stable with respect to water at room temperature in the absence of organic polyisocyanates and hydrolysis accelerating catalysts and, on the other hand, show little or no reactivity with polyisocyanates in the absence of water at room temperature. Accordingly, the condensation products are suitable for use both as latent hardeners for two-component polyurethane systems and as latent hardeners for single-component systems which are cross-linkable under the influence of atmospheric moisture and which contain NCO-prepolymers as the main binder component thereof.
The latent hardeners used in accordance with the present invention are superior to conventional masked diamines, for example according to US-PS No. 3,420,800, both in regard to the storability of the compositions in the absence of water and also in regard to the reactivity thereof in the presence of water and further in regard to the range of potential applications thereof.